The long-term objective of our research is to understand the wide variation in speech perception of individuals with hearing loss who are candidates for hearing aids or cochlear implants, an important challenge that confronts clinicians. We know that speech perception is reflected in auditory pathway physiology. In the auditory cortex, timing, intensity and frequency cues are represented by cortical neural activity and ultimately linked to perceptual performance. Although we can assess the perception of sounds, much less is known about the underlying neurophysiology of the central auditory system. Specifically, the experiments in this study are designed to test the hypotheses that there are differences in the tonotopic organization and the asymmetric activation patterns of the central auditory system in good and poor perceivers of speech. To accomplish our research, we will use a multidisciplinary approach that combines outcome, neurophysiology and functional magnetic resonance imaging (fMRI) in normal listeners and individuals with hearing loss. Measures such as evoked potentials, which are inherently dependent upon neural synchrony, allow us to evaluate the critical components of neural encoding. Neuroimaging techniques such as fMRI, can produce distinct localized images corresponding to auditory cortex activation. Finally, using fMRI, we will investigate whether tonotopic organizational patterns can be identified and relate to speech perception for cochlear implant recipients with a magnetless cochlear implant system. Overall, this research will not only result in a better understanding of the physiology of the auditory cortex, but also a better understanding of the functional significance of tonotopic organization and hemispheric differences in both normal hearing listeners and those with hearing loss.